Direct Observation of Nucleation and Growth Behaviors of Lithium by In Situ Electron Microscopy

Lithium metal anodes are the "Holy Grail" of next-generation high-energy-density Li batteries, yet the nucleation and growth kinetics of Li metal at the nanoscale still remain a myth. Here, by combining in situ electron microscopy and atomistic simulations, we decipher the nanoscale nucleation and growth mechanisms of Li metal on carbon. We find that upon nucleation, Li atoms rapidly aggregate to form droplet-shaped nanoparticles that incline to coalesce through diffusion-mediated fusion. Statistical observation shows that the Li nucleation follows a mixed nucleation mode different from conventional instantaneous or progressive nucleation model. With increased particle size, the droplet-like Li particles transform into faceted crystals driven by surface energy minimization. Atomistic calculations reveal that the size-dependent Li diffusivity facilitates the coalescence and morphological evolution of the Li particles. This liquid-to-solid-like transformation during deposition is completely reversible upon stripping. This work, by unraveling the fundamental nano- and atomic-scale pathways dominating Li metal nucleation and growth behaviors, offers new insights into the deposition/stripping mechanism of Li metal.